Blog for the RepRap project at www.reprap.org - a project to create an open-source self-copying 3D printer. To get all the early posts on this blog with all the images as a single PDF visit this page.

Tuesday, March 14, 2006

Making Version 2

Brett has kindly agreed to knock out a few kits for version 2 of the filament extruder and made some very valuable contributions towards its design. He has access to metal scrap the quality of which I can only dream about.

Here are the first two extruder barrels that he's fabricated. They're made of a good quality stainless steel so we should be in better shape with the colouring of the filament if my guesses about how they're getting coloured is right.

First off, version 2 will have a 1" diameter extruder barrel. The reason for this was my serendepitous discovery of a high quality, extremely cheap barrel heater used by the plastics industry in conventional extruders.

Its a sleeve heater designed to fit over cylindrical bits of plastic extruders to keep molten polymer inside molten. This bad boy prices in at about US$6-7 for a 300 watt heater. It can be bought for either 110 v or 230 v AC mains power. The cartridge heater it replaces costs closer to US$10-15.

The only drawback to this kind of heater is that it makes the use of a bimetallic thermostat as we were able to do with version 1 impossible for the simple reason that there is no place on an extruder barrel covered by this heater to mount one. That is not a big problem in that the controller for the Mk II extruder that is being used on the RepRap itself already makes use of a thermistor temperature sensor for control. I am sending along a kit of pieces for version 2 to Simon who has kindly agreed to morph the Mk II extruder controller board design into one that can handle version 2.

The polymer pump will be made, according to Brett, from 1.25"x1.25" stainless steel bar stock.

Overall, version 2 will weigh about half of what version 1 did. This is especially important in the extruder barrel in that it will have a much smaller thermal intertia than the version 1 did. The sleeve heater should also make for a much more evenly distributed thermal input to the polymer.

I should correct this: The heated barrels are made of an extremely *low* grade of stainless steel. He merely thinks it's great stuff because he's used to working with cold rolled steel, which makes even the worst stainless look good.